Start control

ABSTRACT

Transmission and engine control means for a vehicle wherein the engine is connected through at least one friction clutch to a transmission having a positively geared power train therethrough. A low speed governor is provided to sense an engine speed at or shortly below idling speed and functions to increase fuel supply to the engine as same is lugged down for maintaining, within the capacity of the engine, at least said selected minimum speed. Further, means are provided responsive to the position of the throttle control, such as the accelerator pedal, for modulating the engagement pressure of said clutch in response to the position of such throttle control, progressive opening of the throttle effecting progressive increase in the torque transmitting capacity of the clutch, whereby the torque transmitting capacity of the clutch is under all throttle settings maintained at a value a little greater than the load torque normally applied thereto at such throttle setting. If desired, further means may be provided for deactivating and disengaging said transmission clutches entirely when the throttle is in its idling position and the vehicle is either at standstill or at a speed below a selected value.

This is a division of application Ser. No. 404,221 filed Oct. 9, 1973,now abandoned.

FIELD OF THE INVENTION

This invention relates to transmission control means and particularly toa system for enabling a vehicle, having a spur gear transmissionincluding at least one gradually engageable clutch between giventransmission ratio gears and the engine, to start smoothyl undersemi-automatic control from standstill and without possibility ofstalling, excessive acceleration, jerking on shifting or other abuse onthe part of the operator.

BACKGROUND OF THE INVENTION

The invention arises out of long continued efforts to provide vehicle,and especially truck, transmissions with the flexibility of full manualcontrol by the operator on the one hand and on the other hand themaximum convenience and freedom from abuse by the operator of fullyautomatic transmissions.

In connecting a geared transmission (as distinguished from a torqueconverter) to a prime mover, it has long been known to accomplish samethrough a friction clutch. This has been common for many years in bothpassenger car and truck installations. It has the well recognizedadvantage of giving the operator complete and positive control over therate of buildup of torque output by the transmission and requiresminimum apparatus but, particularly for truck installations, requires ahigh level of both competence and carefulness on the part of theoperator. All of this has been well known virtually from the beginningof automotive practice. The engine can be stalled if the clutch isengaged more rapidly than can be handled by the buildup of engine outputresulting from simultaneous depression of the accelerator pedal or onthe other hand the vehicle can be caused to generate excessive strainswithin its driving train if shifts are made jerkily or even sometimes ifthe accelerator pedal is depressed rapidly and suddenly while the clutchis simultaneously engaged suddenly. A competent and careful driver canand does successfully control both the engagement of the clutch anddepression of the accelerator pedal but a driver of less competencyand/or carefulness can abuse a vehicle, especially a truck, seriously.This problem is recognized as particularly acute where it is rememberedthat an internal combustion engine, whether of the spark ignition orcompression ignition type, will at a given throttle setting firstincrease its torque output somewhat as its speed is reduced from themaximum speed for such throttle setting and then diminish the torqueproduced as its engine speed is still further reduced. Thus, when anengine is excessively loaded so that its speed diminishes below acertain point, its torque output likewise diminishes which acceleratesthe rate of speed reduction and the progression toward stalling proceedson a rapidly steepening curve. All this is well known and is normallycompensated for by the driver by depression of the accelerator pedal andincreasing the fuel supply to the engine. However, this must be doneskillfully for an excessive depression of the accelerator pedal willexcessively and suddenly increase the torque output of the engine andcause same to jerk with resulting unpleasant effects on the driver (andpassengers if any), on the payload carried by the vehicle and on thedrive train.

This being undesirable for obvious reasons, particularly for heavy dutyvehicles, it has long been desirable to provide automatic means foreffecting the starting functions of the vehicle but protecting saidvehicle from either careless and/or incompetent handling. In an attemptto meet this objective, some workers in the field have providedautomatic transmissions wherein the control functions are taken awayfrom the driver completely and are programmed according to somepredetermined ideal starting situation. This works well enough in mostinstances but such transmissions are expensive, require a substantialamount of maintenance and because of their rigidly preprogrammedcharacteristics, sometimes fail to be adaptable to certain specificoperating requirements. Other workers in the field in an attempt to meetthe foregoing named objective have utilized torque converters betweenthe prime mover and a transmission. This likewise operates well enoughbut it is also expensive, requires considerable maintenance and is thesource of considerable power loss for well-understood reasons.

It is therefore still desirable to provide if possible control meansprimarily adaptable to a starting situation for a transmission havingpositively interengageable gear teeth, such as spur gear teeth, andwherein the transmission is connected to the prime mover by at least onefriction clutch which, when fully engaged, provides a positive drivefrom the prime mover to the transmission and yet to control suchinterengaging means by apparatus which will be consistent with controlmeans to which drivers are already accustomed and which will insureagainst the undesirable consequences of careless or incompetent handlingof presently known fully manual (pedal) operated apparatus. In at leastthe broadest concept of the invention it is immaterial whether thefriction clutch be a single clutch located between the prime mover andthe transmission or whether same be friction clutches within thetransmission by which the desired gear ratios are selected for operativeconnection between the input and output shafts thereof.

Accordingly, the objects of the invention include:

1. To provide a control device for a vehicle, particularly adaptable forthe starting thereof, which will permit the use of a positively gearengaged transmission utilizing a friction clutch for energizing same butwill protect the vehicle and particularly the power train thereofagainst the consequences of careless and/or incompetent operation.

2. To provide apparatus, as aforesaid, which will insure that sufficientfuel is supplied to the prime mover regardless of the extent to whichthe operator has in a given instance depressed the accelerator pedal toinsure that the engine under the starting conditions actually imposed ata given time will have sufficient fuel to produce, within its operatingcapacity, the torque required and avoid stalling.

3. To provide apparatus, as aforesaid, which will be immobilized whenthe vehicle is at standstill or moving at less than a predeterminedspeed and the throttle is at its idle setting, whereby to insure againstimposing driving torque onto the drive train of a standing orsubstantially standing vehicle when same is not desired.

4. To provide apparatus, as aforesaid, which is particularly adaptableto use with a diesel engine as the prime mover.

5. To provide apparatus, as aforesaid, which is particularly adaptablefor use with heavy vehicles, such as trucks.

6. To provide apparatus, as aforesaid, which is relatively simple andhence economical both in the original manufacturing thereof and in themaintenance thereof.

Other objects and purposes of the invention will be apparent to personsacquainted with apparatus of this general type upon reading thefollowing disclosure and inspection of the accompanying drawings.

In the drawings:

FIG. 1 is a speed torque curve of a typical diesel engine which will bereferred to for further discussing the problem solved by this apparatusand for describing the function of the apparatus.

FIG. 2 is a schematic diagram of apparatus embodying the invention.

SUMMARY OF THE INVENTION

Assuming the invention to be applied as is preferable to a positivegear, as a spur gear, transmission through ratio determining frictionclutches, there are provided suitable ratio control devices, normallypressure fluid valves, which are selectable by a suitable selectordevice. The power input to said ratio control devices is subject to twoparallel connected energizing devices, switches or valves asappropriate, which devices may for example be normally in a powerinterrupting condition and may be rendered power conductingindependently of each other, one by opening of the throttle to otherthan idling speed and the other by attainment by the vehicle of a speedin excess of a selected low speed, such as three miles per hour. Anothercontrol is connected to the throttle control, normally the acceleratorof the vehicle, and includes a pressure regulator which acts to controlthe pressure applied through said ratio control devices to the clutches.Thus, opening of the throttle (depression of the accelerator) willprogressively increase the pressure applied to whichever one of thetransmission clutches (or to the main clutch if such is used) isactivated at a given moment. In addition there is provided a low speedgovernor to maintain the engine at at least an idling speed, which willopen the throttle as the engine is pulled down from normal driving speedto try to maintain same at least at such idling speed and prevent itfrom stalling.

DETAILED DESCRIPTION

Referring to FIG. 2, there is diagrammatically shown a system of engineand transmission controls embodying the invention. Inasmuch as theindividual components of these controls may be any of many presentlywell known types and forms, the details are not given but may besupplied as appropriate to a given installation by any skilled worker inthe art.

The throttle control 1 is here shown as a conventional foot acceleratorwhich is connected by conventional linkage 2 to the control lever 5 of afuel supply valve 3, here assumed to be the fuel valve of a compressionignition engine. The low speed governor 4 is driven in any conventionalmanner in response to engine speed, such as by a drive gear 6, and theslider 7 thereof responds in a conventional manner to the verticalposition of the fly balls 8 to operate one arm 9 of a bell crank 10whose other arm 11 acts through a further linkage 12 also onto thecontrol lever 5 of the fuel valve 3. Suitable motion absorbing means(not shown) are provided to enable the linkages 2 and 12 to act eachindependently of the other onto the lever 5. Thus, in any conventionaland presently known manner the position of the fuel supply valve isdetermined either by the position of the throttle control 1 or by theposition of the governor 4, each acting independently of the other. Allof this is conventional, is well known and requires no furtherexplanation.

In a typical installation embodying the invention and assuming for anillustrative but not limiting embodiment that the transmission inquestion utilizes a plurality of ratio selecting pressure responsivefriction clutches, and that there is no main clutch or at least noneconnected into this system, there will be provided a plurality of ratioselecting valves, here exemplified by the four valves 16, 17, 18 and 19.Each of said four valves is appropriately controlled, here by solenoids21, 22, 23 and 24, respectively. Each of said solenoids is energizablefrom the source S acting through parallel connected energizing controldevices, either switches or valves as appropriate, 26 and 27, thenthrough a manually operable selector 28. The position of the selectorhandle 29 is determined in a conventional manner by the operator of thevehicle and acts through appropriate energy transfer means, conductorsor conduits as appropriate, here indicated at 31, 32, 33 and 34 toenergize an appropriately selected one of the above-mentioned solenoids21-24.

A suitable source 41 of pressure fluid is conducted by a suitableconduit 42 to a pressure regulator 43 and thence by the conduit 44 toconduits 46, 47, 48 and 49 which are respectively connected, in onesetting of said valves 16-19, through the valves 16-19 back to the lowpressure side of the fluid system. In the other setting of said valves,the pressure conduits 46-49 are respectively connected through conduits56-59 to the above-mentioned pressure responsive friction clutches forengaging a desired ratio of the transmission. Thus, when the selectorhandle 29 is in the position shown in FIG. 2 and each of the solenoids21-24 is deenergized, the valves 16-19 will be in the deenergizedpositions shown and the fluid pressure generated at the source 41 willmerely return to the low pressure side of the pressure system. However,when, for example, the handle 29 is moved to the first speed positionthe energy conducting means 33 will energize the solenoid 23 to shiftthe valve 18 into its energized position (leftwardly as appearing inFIG. 2) so that pressure fluid appearing in the line 48 will beconducted through conduit 58 to the clutch operating means associatedwith the first gear speed of the transmission and said transmission willthen in a conventional manner assume its first speed condition.

The manner by which such clutches may control a transmission for thispurpose is already well known and is fully set forth by many patents, ofwhich U.S. Pat. No. 2,648,992 to J. G. Vincent is an example, and henceneeds no further detailing.

In the meantime the pressure regulator includes an appropriate meanssuch as an adjustable orifice device 45 which responds to the positionof the throttle control 1 for controlling the pressure fluid escapingtherethrough to a line 51 and thence back to the low pressure side ofthe pressure system and thereby determining the magnitude of pressureappearing in the line 44. This determines the pressure appearing in eachof the lines 46-49 and thereby on whichever of the transmission clutchesmay be connected thereto by energization of the appropriate ones of thevalves 16-19.

It is common for transmission clutches which are operated by pressurefluid to require a short time for the operating cylinders thereof tofill before pressure builds up to the value set by the pressureregulator. Therefore, the engine response to the depression of thethrottle may be faster than the clutch pressure and torque build up.However a very short time after the engine speeds up, the clutch torquebuilds up to the pressure regulator value so that the clutch torquecapacity exceeds the maximum engine torque for the specified throttlesetting.

Any appropriate linkage generally indicated at 52 will connect thethrottle control 1 to the energy control device 26 by which same iscaused, or permitted, to assume an energy blocking condition when thethrottle control is at or near its zero (idling) position and move to anenergy conducting condition when the throttle control 1 is moved apredetermined distance away, usually only a very small amount, from saidzero or idling position.

A device 53 of any known type is provided responsive to transmissionoutput (or vehicle) speed and connected to the energy control device 27.The arrangement is such that the device 27 is in an energy blockingposition when the vehicle is at or below a relatively low predeterminedspeed, such as three miles per hour, but the device 27 will becomeenergy conducting when the vehicle speed exceeds said predeterminedvalue.

In the preferred embodiment illustrated in the drawings, the powersupply S and the means connecting same through the selector 28 to thevalve controls 21-24 are electrical, the conducting means 46-49 and56-59, respectively, conduct a pressure fluid, either air or hydraulic,and the connecting means 2, 12, 50, 52 and 55 are mechanical. However,the selection of the particular form of power transmitting means is amatter of choice on the part of the designer to meet given operatingconditions and any of these power transmitting means may be electrical,pressure fluid or mechanical as desired and appropriate in a giveninstance.

OPERATION

Assuming for purposes of illustration that the system herein describedis used with a compression ignition type of engine, reference is made toFIG. 1 for illustration of the normal operating relationship thereof.Horizontal distances therein indicate engine speed in rpm's and verticaldistances indicate the torque values. The line A indicates engine idlingspeed and the line B indicates normal rated speed of 2100 rpm's. Line Cindicates the torque-speed relationship of the engine at one-quarterthrottle position and shows that under normal operating conditions thetorque increases at first as rpm's increase to an optimum point and thendecreases slightly as the rpm's continue to increase. Thus, as loadappears on the vehicle which is operating at 2100 rpm's and the engineresponds thereto by slowing down, the torque at first increases andassists the engine in meeting the additional load applied. However, whenthe optimum point is passed, then the slowing and decrease in torque areincreasing and progressive in response to each other and the vehicle, ifnot properly handled, will quickly stall. The torque developed by theengine at any given speed will, of course, depend upon the throttlesetting and to insure that the torque developed at any given throttlesetting for a range of speeds appropriate thereto will be transmitted tothe transmission gearings, but without jerking, during shifts or if theaccelerator should be depressed too rapidly and too suddenly, it isdesirable that the torque transmitting capacity of the clutch remainabove, but no more so than necessary, the torque generating capacity ofthe engine for all speeds at a given throttle setting. This is indicatedby the broken line D in FIG. 1, which line indicates that the clutchshould have a torque transmitting capacity which is just slightlygreater than the maximum engine torque at the specified throttlesetting.

Turning now to FIG. 2, with the vehicle at rest and the engine idling,the throttle control 1 will be at its zero position to open the switch26 and the speed sensor 53 will indicate zero vehicle speed and open theswitch 27. Thus, all of the solenoids 21-24 are deenergized and thevalves 16-19 are in the positions shown in FIG. 2. Thus, none of theclutches are energized and the transmission is in its neutral position.This will be true regardless of the position of the control knob 29inasmuch as no power is being supplied to the selector. Thus, thecontrol knob can be moved into any desired gear position, such as firstposition, without causing any shifting or other activation of thetransmission to take place.

Now as the throttle control 1 is depressed, the switch 26 will be closedand energy from the power source S will be supplied to the selector 28and, with the control handle 29 in its first gear position, energy willbe supplied to the solenoid 23 for shifting the valve 18. This appliespressure fluid to the first speed clutch for effecting engagementthereof. At the same time the depression of the throttle control 1 willact through the pressure regulator 43 to increase the pressure withinthe line 44 by an amount which is a function of the depression of saidthrottle control, and thereby apply a similarly increasing force forcausing engagement of the first gear clutch.

It will be evident, in view of the foregoing, that the parameters arearranged so that at a given throttle position the torque capacity of thefully engaged clutch will be somewhat higher, for example 10-30% higher,than the engine torque applied thereto under normal operation in thegear position in question. Further in the illustrated embodiment the oilpressure supplied to the clutch cylinders is assumed to be a function ofthe throttle depression so that at any selected throttle setting theclutch torque curve (D in FIG. 1) is a straight line whose position(magnitude) is determined by the throttle setting but which isindependent of engine speed.

Since the torque transmitting capacity of the engaged transmissionclutch is determined by the position of the accelerator pedal, it willbe understood that under starting conditions (i.e. with the vehicle atstandstill and the throttle only a little depressed) the clutch willslip in the same manner as with pedal control and the engine speed willincrease. After a short time delay to fill the operating cylinder of theclutch, the clutch pressure and torque capacity will increase to exceedthe engine torque and start to lug the engine down in speed. The clutchwill continue to slip as the clutch torque increases but the vehiclewill start to move.

As the vehicle gathers speed, the vehicle will gain speed with respectto the engine and hence the clutch slippage diminishes. The vehicle isthus started smoothly and without jerking in the same manner asaccomplished by manual control with a skilled and careful operator.

If, during the starting operation, the vehicle meets a substantialresistance, such as a steep incline, the torque requirements areincreased and the engine is lugged down toward its idling speed. Again,a skilled operator will increase the fuel supply by depression of theaccelerator but if the operator is not skilled or is inattentive, whenthe engine slows to its idling speed the governor 4 will sense thiscondition and cause the fuel supply to increase sufficiently to supplythe torque required and thus prevent stalling. In other words, thedecrease in speed will be halted at the idle line A and the torque willbe increased along said line up to the point permitted by the clutchtorque line D, thus preventing engine stalling. As the vehicle gathersspeed the vehicle will gain speed with respect to the engine, clutchslippage will diminish and the vehicle will be started smoothly.

During shifting the torque applied to the engaged clutch (in onedirection or the other depending on whether the shift is an upshift or adownshift) will depend upon the position of the accelerator pedal. Thus,the clutch torque required to effect the synchronization of the shiftwill be a little greater than the engine torque output at the giventhrottle position and thereby provide a smooth shift.

If during operation the vehicle should encounter a downward slope sothat the operator releases the accelerator pedal 1 completely andthereby opens switch 26, this will still not return the transmission toneutral but will instead respond to the vehicle speed sensing means 53acting through the switch 27 to maintain the transmission in theoperator selected gear and thereby utilize the engine drag for thedownhill operation.

However, when the vehicle is subsequently stopped and the throttle pedal1 returned to its zero position, then both switches 26 and 27 are openedand the solenoids 21-24 will all be deactivated. This returns the valves16-19 to their de-energized position and returns the transmission to itsneutral position and same will occur even though the selector knob 21remains in a ratio selecting position.

If and as the throttle is advanced to generate progressively more torqueas needed by the engine, the regulator 43 will respond to the throttleposition and cause progressively more pressure to appear in line 44 andconsequently progressively more pressure to appear onto whatevertransmission clutch is energized at a given time. Thus, said clutches assame are engaged from time to time will always be engaged withsufficient force to transmit whatever torque is required and availablefrom the engine in response to the throttle position.

However, if the operator advances the throttle very suddenly, theabove-mentioned slowing of the response thereto of the engaging clutchto a point slightly behind that of the engine, will permit said clutchagain to initially slip and then stabilize as the vehicle gathers speedin response to the engine. This again avoids jerking, especially in lowspeed transmission settings, which thus avoids resultant strain on thedrive train.

It will be further recognized that the use of this system will in no wayinhibit the normal functioning of friction clutches to render smooth theshifting from one speed ratio to another in a conventional manner butwith positive locking of the parts during normal operation to attain thehigher efficiency already known to exist in such an arrangement.

In the foregoing embodiment, each of the pressure lines 56-59 has beenassumed to lead to and operatively connect with a clutch whoseengagement effects a selected ratio condition in the transmission. Spurgear transmissions with non-positive, as frictional or magnetic,clutches to engage gear sets or planetaries with frictionally engagingbands are examples of such transmissions. If, however, the transmissionis of a type utilizing positive, as jaw, clutches (normally withsynchronizers) as ratio establishing clutches, and only a singlenon-positive clutch as the main clutch between the transmission and theprime mover, then said operating lines 56-59 will extend to conventionaland presently known pressure responsive means for appropriatelyoperating and sequencing both the main clutch and the ratio establishingclutches in any presently known and conventional manner.

While one specific item of the apparatus has been chosen andschematically illustrated for disclosure purposes, it will be recognizedthat at least the broader aspects of the invention can be embodied inother arrangements of apparatus and the hereinafter appended claims willbe understood as applicable thereto excepting as said claims by theirown terms require otherwise.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A control system for amulti-ratio transmission connectable at its input to a prime mover inresponse to actuation of at least one of a plurality of ratio-selectingclutches and at its output to a load, said system comprising:a manuallymovable throttle means having an idle position and operative to increasethe speed of said prime mover in response to manual movement away fromsaid idle position; manually movable selector means having an inactiveposition and a plurality of active positions each corresponding to atleast one of said clutches; first means actuated by manual movement ofsaid throttle means; and means operative to actuate at least one of saidclutches in response to movement of said selector to an active positioncorresponding to said at least one of said clutches and actuation ofsaid first means.
 2. The system of claim 1, further includingsecondmeans operative in response to the output speed of said transmissionexceeding a minimum to override said first means and allow saidoperative means to maintain actuation of said at least one of saidclutches independent of the position of said throttle means.
 3. Thesystem of claim 1, wherein said first means is connected in series withsaid manually moveable selector means.
 4. The system of claim 2, whereinsaid second means is connected in parallel with first means and saidselector means is connected in series with said first and second means.5. The system of claim 1, further includingsecond means operative tooverride said first means for maintaining said at least one of saidclutches in an actuated condition independent of the position of saidthrottle in response to the output of said transmission exceeding apredetermined speed; and control means responsive to the position ofsaid throttle means for increasing the torque transmitting capacity ofsaid at least one of said clutches in proportion to manual movement ofsaid throttle away from said idle position.
 6. The system of claim 5,further includinglow speed governor means operative to maintain saidprime mover at a predetermined minimum speed.
 7. A control system for amulti-ratio transmission connectable at its input to a prime mover inresponse to fluid pressure actuation of at least one of a plurality ofratio-selecting clutches and at its output to a load, said systemcomprising;manually moveable throttle means having an idle position andoperative to increase the speed of said prime mover in response tomanual movement away from said idle position; a source of pressurizedfluid; passage means for connecting said source to said plurality ofclutches; manually moveable selector means having an inactive positionand a plurality of active positions which each correspond to one of thetransmission ratios; first means actuated in response to manual movementof said throttle means away from said idle position; valve meansassociated with said passage means and operative to allow actuation ofat least one of said clutches by allowing flow of said pressurized fluidto said at least one of said clutches in response to movement of saidselector to an active position corresponding to said at least one ofsaid clutches and actuation of said first means.
 8. The system of claim7, further including;second means operative to override said first meansand allow continued flow of said pressurized fluid to said at least oneof said clutches in response to the output of said transmissionexceeding a predetermined speed.
 9. In a wheeled land vehicle a controlsystem for a multi-ratio transmission connectable at its input to aprime mover in response to fluid pressure actuation of at least one of aplurality of ratio-selecting, friction clutches and at its output towheels of said vehicle, said control system comprising:manually moveablethrottle means having an idle position and operative to increase thespeed of said prime mover in response to manual movement of saidthrottle means away from said idle position. a source of fluid passagemeans for connecting said source to said plurality of clutches; pressureregulating means responsive to the position of said throttle means forincreasing the pressure of said fluid in said passage means inproportion to manual movement of said throttle away from said idleposition; manually moveable selector means having an inactive positionon a plurality of active positions which each correspond to at least oneof said ratio-selecting clutches; first means actuated in response tomanual movement of said throttle means away from said idle position;valve means associated with said passage means and operative to allowactuation of at least one of said clutches by allowing flow of saidpressure regulated fluid to said at least one of said clutches inresponse to movement of said selector to a corresponding active positionand actuation of said first means; low speed governor means responsiveto the speed of said prime mover for preventing a decrease in said primemover speed below a predetermined minimum and for increasing the torquetransmitting capacity of said prime mover and accelerating said vehicleto a speed corresponding to at least the minimum prime mover speed. 10.The control system of claim 9, further including:second means operativein response to the output speed of said transmission exceeding a minimumto override said first means and allow continued flow of said pressureregulated fluid to said at least one of said clutches independent of theposition of said throttle means.
 11. The system of claim 10, whereinsaid first means is connected in series with said manually moveableselector means.
 12. The system of claim 11, wherein said second means isconnected in parallel with said first means and said selector means isconnected in series with said first and second means.
 13. In controlmeans for a multi-speed transmission, connectable at its input throughat least one selected one of a plurality of friction clutches to anengine and connected at its output to a load, comprising incombination:a manual throttle connection to engine fuel control means; apressure regulator responsive to the position of said manual throttleconnection to said engine fuel control means so that a progressivelymore fuel position of said throttle connection corresponds to aprogressively greater development of pressure by said pressureregulator; a plurality of valves, including control devices for eachthereof and means including said pressure regulator for connecting ofsource of pressure to each of said valves whereby one condition of eachof said valves will cause same to conduct such pressure to one of saidclutches for engaging same and the other condition of said valves willeffect deenergization of said one of said clutches; control meanseffecting energization of a selected one of said valves for connectingsaid pressure to a selected one of said clutches; and a pair of parallelconnected power transmitting devices, one thereof being conditioned tocause opening of said selected transmission clutch when the throttle isnear its idling position and to effect closing of such clutch when thethrottle control moves away from its idling position and the other ofsaid devices being responsive to the speed of the vehicle in such amanner as to place said clutch in power transmitting condition when theoutput speed of the transmission is in excess of a predetermined valueand to place said transmission in non-power transmitting condition whenthe output speed of the transmission is less than said predeterminedvalue.
 14. In control means for a multi-speed transmission, connectableat its input through at least one selected one of a plurality offriction clutches to an engine and connected at its output to a load,comprising in combination:a manual throttle connection to engine fuelcontrol means; a pressure regulator responsive to the position of saidmanual throttle connection to said engine fuel control means so that aprogressively more fuel position of said throttle connection correspondsto a progressively greater development of pressure by said pressureregulator; a plurality of valves, including control devices for eachthereof and means including said pressure regulator for connecting asource of pressure to each of said valves whereby one condition of eachof said valves will cause same to conduct such pressure to one of saidclutches for engaging same and the other condition of said valves willeffect deenergization of said one of said clutches; and a minimum speedgovernor responsive to the output speed of said engine and meansconnecting same to said engine fuel control means for increasing saidengine fuel independent of said manual throttle connection when saidengine speed drops below a predetermined speed due to increased loadappearing at the output of said transmission.
 15. The system of claim 1,further includingcontrol means responsive to the position of saidthrottle means for increasing the torque transmitting capacity of saidactuated clutch in proportion to manual movement of said throttle meansaway from said idle position; and low speed governor means operative tomaintain said prime mover at a predetermined minimum speed.
 16. Thedevice of claim 14 including a minimum speed governor responsive to theoutput speed of said engine and means connecting same to said enginefuel control means for increasing said engine fuel independent of saidmanual throttle connection when said engine speed drops below apredetermined speed due to increased load appearing at the output ofsaid transmission.
 17. The system of claim 8, wherein said prime moveris a combustion engine and said manually moveable throttle meansoperates a fuel supply valve for varying the fuel flow to said engine,said system further including;pressure regulating means responsive tothe position of said throttle means and operative to increase thepressure of said pressurized fluid in proportion to manual movement ofsaid throttle means away from said idle position, thereby increasing thetorque transmitting capacity of said at least one of said clutches forselected actuation in proportion to the torque transmitting capacity ofsaid prime mover; and low speed governor means operative to increase thefuel flow to said engine by said fuel supply valve independent of saidmanually movable throttle means for maintaining said engine at apredetermined minimum speed.
 18. The system of claim 17, wherein saidfirst means is connected in series with said manually moveable selectormeans.
 19. The system of claim 18, wherein said second means isconnected in parallel with said first means and said selector means isconnected in series with said first and second means.